1. Field of the Invention
The role of shaft kilns for calcining limestone and the like is well known in the prior art. Such kilns in the prior art are known as "annular shaft Kilns" or "double inclined kilns". At present, most all double inclined shaft kilns in operation, utilize gaseous fuels as a means of firing the systems. The few exceptions utilize a coal stoker to generate hot gases for such systems. The problems associated with the coal stoker kilns of the prior art include contamination from the solid fuel injected directly into the system, high capital cost for the stoker arrangement, increased power consumption of prior art systems in the necessity to pulverize the solid fuel utilized, the narrow and specific type of solid fuel material suitable for use in the prior art systems, and the lack of temperature control in the coal stoker systems of the prior art. In addition, annular shaft kilns are also fired only with gaseous fuels and experimental work on direct injection of pulverized coal into such units in order to accommodate the less expensive fuel has created the problem of ash contamination and sulfur absorption, particularly when producing lime or dolomite for use in the steel industry.
The invention defined herein is concerned with an improved apparatus and sequence of processing steps which will more efficiently utilize the capabilities of shaft kilns of the annular and double inclined type.
2. Description of the Prior Art
Kilns known as "annular shaft kilns" or "double inclined kilns" are generally known in the prior art and are illustrated and described in one or more of the following U.S. Pat. Nos. 3,204,936; 3,658,308; 3,695,595; 3,765,827; 3,856,436; 4,025,293; and 4,254,221, the disclosures of all of which are incorporated herein by reference.